For display devices such as liquid crystal display devices, color filters are widespread for the purposes of color image display, reflectance reduction, contrast adjustment, spectral characteristic control, and the like. In order to produce a color filter, colored pixels need to be formed on a substrate so as to be aligned in a matrix. In order to form the colored pixels on the substrate, photolithography method is typically used widely. Specifically, photosensitive resin (hereinafter, referred to as a “resist”) having coloring agent such as pigment and dye dispersed therein is firstly applied to a substrate by using a spin coating or a spinless coating method, and thereafter excessive solvent in the resist is removed by pre-baking. Subsequently, a photomask having an opening pattern (in the case of a negative type resist) corresponding to the colored pixels is used to expose the resist to light for representing the opening pattern. The exposure to light is performed by, for example, applying active energy ray from a high-pressure mercury lamp acting as a light source, to the resist through the photomask. Finally, the resist and developer are brought into contact with each other, to dissolve and remove unnecessary resist, and thereafter rinsing and postbaking are performed. These are repeated the number of times corresponding to the number of colors of the colored pixels.
In order to expose the resist to light for representing the opening pattern, a proximity exposure (close exposure) method in which the entire surface of the substrate can be exposed to light at one time may be used. In an exposure device used in the proximity exposure method, distribution of illuminance of light applied from an ultrahigh pressure mercury lamp acting as a light source is made uniform by using a fly-eye lens. Thereafter, light emitted from the fly-eye lens is transformed into parallel light beams by using a collimator lens. The photomask is positioned so as to be spaced from the substrate (to form a gap) by several tens of μm to several hundreds of μm. The parallel light beams are applied to the entire surface of the photomask. As a result, the opening pattern is transferred to the resist on the substrate at the same magnification.
The exposure device used for the proximity exposure method has a simple device structure as compared to, for example, an exposure device including a projection optical system. Therefore, use of the proximity exposure method is advantageous in that cost for the devices can be reduced. Further, the same area as that of the photomask can be exposed to light at one time. Therefore, use of a photomask corresponding to a size of an exposed area on the substrate is advantageous also in that process tact for the exposure process steps can be reduced.
However, in recent years, sizes of a color filter substrate and a TFT (Thin Film Transistor) substrate included in a liquid crystal panel tend to be increased. Exemplary substrate sizes are 1500 mm×1800 mm (the sixth generation), 2160 mm×2400 mm (the eighth generation), and 2850 mm×3050 mm (the tenth generation). The increase in size of a color filter substrate, and the like inevitably require increase in size of a photomask and increase in size of an illumination optical system of the proximity exposure device. As a result, a problem arises that production cost for photomasks is increased. Further, the increase in size of a color filter substrate leads to enlargement of a light-applied area, so that a problem also arises that energy efficiency of the applied light is reduced.
In order to solve the above-mentioned problems, an exposure method (hereinafter, referred to as a “maskless exposure method”) may be used in which a pattern is directly formed on a substrate by using laser light without using a photomask. In this method, while laser light is being applied to the resist on the substrate, the laser light is modulated as necessary according to a pattern to be formed. Therefore, the maskless exposure method is advantageous in that use of expensive photomasks is unnecessary. However, for the maskless exposure method, development of a modulation device for modulating the laser light and/or a resist suitable for laser light to be used is difficult. The maskless exposure method has a lot of problems to be solved for realizing exposure to light for a color filter having a large size with reduced production cost.
Therefore, a method (hereinafter, referred to as a “small mask continuous exposure method) may be used in which a plurality of small masks are aligned, and a resist on a substrate is repeatedly exposed to light for representing an opening pattern of a photomask while the substrate is being conveyed. In the small mask continuous exposure method, a blind shutter positioned between the photomasks and a light source is opened or closed in synchronization with the conveying of the substrate, and thus switching between application of light to the resist and shielding of the resist from the light is controlled as necessary. As a result, the resist on the substrate is freely separated into an area (hereinafter, referred to as an “exposed area”) which is exposed to light and an area (hereinafter, referred to as an “unexposed area”) which is not exposed to light.